CH653808A5 - NON-AQUEOUS CELL COMPRISING A LIQUID CATHODE, AN ACTIVE ANODE, A CATHODE COLLECTOR AND A SEPARATOR ARRANGED BETWEEN THE ANODE AND THE COLLECTOR. - Google Patents

Description

The invention relates to a non-aqueous cell comprising a liquid cathode such as an oxyhalide, a halide and / or liquid sulfur dioxide, an active anode such as lithium, a cathode collector such as a carbon collector, and a separator disposed between said anode and said collector, and wherein said separator comprises a uniform mixture of 85 to 95% by weight of glass fibers having a substantially uniform length, and 15 to 5% by weight of binder.

The continual development of portable electrical devices such as tape recorders and players, radio transmitters and receivers and the like, creates a continuing demand for the development of reliable batteries with long service life , for their operation. Newly developed electrochemical cell systems, which have a long service life, use highly reactive anode materials such as lithium, sodium and the like, in conjunction with non-aqueous, energy density cathode materials high and a suitable salt.

It has recently been indicated in the literature that certain materials are capable of acting both as an electrolyte support, that is to say as a solvent for the electrolyte salt, and as an active cathode for a battery. non-aqueous electrochemical. British Patent No. 1409307 describes a non-aqueous electrochemical cell comprising an anode, a cathode collector and a cathode-electrolyte, said cathode-electrolyte comprising a solution of an ionically conductive solute dissolved in an active cathode depolarizer, where said depolarizer of active cathode includes a liquid oxyhalide of an element of group V or group VI of the periodic table. The periodic table is the periodic table of the elements as given on the inside page of the back cover of "The Handbook of Chemistry and Physics", 48th ed., The Chemical Rubber Co., Cleveland, Ohio, 1967-1968. For example, such non-aqueous cathode materials may include sulfuryl chloride, thionyl chloride, phosphorus oxychloride, thionyl bromide, chromyl chloride, vanadyl tribromide and selenium oxychloride .

Another class of liquid cathode materials may be the halides of an element from group IV to group VI of the periodic table. For example, such a non-aqueous cathode material may include sulfur monochloride, sulfur monobromide, selenium tetrafluorare, selenium monobromide, thiophosphoryl chloride, thiophosphoryl bromide, vanadium pentafluoride, tetrachloride lead, titanium tetrachloride, sulfur pentafluoride, monobromuretri-tin chloride, tin dibromuredichloride and tribromide-tin monochloride.

However, a possible disadvantage of using a liquid cathode such as thionyl chloride is that, if it is not distributed uniformly along the surface of an anode, such as lithium, through of a separator, non-uniform consumption of the anode may then appear and may result in a low output voltage, in particular at high discharge rates, and longer voltage delays after storage. In addition, a non-uniform distribution of the liquid cathode which may result from non-uniform wetting of the separator by the liquid cathode can cause non-uniform dissolution of the anode. This non-uniform dissolution of the anode can cause the formation on the anode of high points and plates which can have the possible result of localized heating during charging (abusive condition) and can lead to the possibility of a fusion of the anode at these separate points. This can lead to violent ventilation of the battery or even disassembly of the battery. It is believed that the non-uniform wetting of the separator by the liquid cathode is the source of a reduction in the useful power of the cell.

The subject of the invention is therefore a battery comprising a liquid cathode with a separator which can be wetted uniformly by the liquid cathode, thus resulting in an improved behavior when discharging the battery, in particular during a discharge at high flow rate, and improved battery safety features.

The invention relates to a non-aqueous cell comprising a liquid cathode, an active anode, a cathode collector, and a separator arranged between said anode and said collector, characterized in that the separator comprises a uniform mixture of 85 to 95% in weight of glass fibers and 15 to 5% by weight of binder, said glass fibers having a length of 3.18 to 12.70 mm and a diameter of 2 to 8 (xm. and in the fact that 90% of the fibers differ by less than 20% from the average fiber length and differ by less than 20% from the average fiber diameter.

The separator used in the cell according to the invention is preferably porous in order to be able to efficiently absorb the liquid cathode. In general, a porosity of 25% or more, preferably about 50 to 75%, is suitable for most battery applications. Separated him5

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They should have about 85 to 95% by weight of glass fibers and about 5 to 15% by weight of binder, and preferably about 91 to 94% by weight of glass fibers and about 9 to 6% by weight of binder. An amount of glass fibers greater than 95% by weight would not provide a material suitable for handling when using a conventional binder, while an amount of glass fibers less than 85% by weight would not provide sufficient material to effectively absorb the liquid cathode to achieve uniform distribution of the liquid cathode between the anode and the cathode collector. The size (length and diameter) of the glass fibers must be substantially uniform so that at least 90% of the glass fibers have a length and a diameter which differ by less than 20% from the average length and diameter of the glass fibers , and preferably 95% or more of the glass fibers have a length and diameter in the range of 20%. Preferably, the length and diameter of at least 90% of the glass fibers differ by about less than 10% from the average length and the average diameter of the glass fibers and, more preferably, 95% or more of the glass fibers fall in this range. The glass fibers should be between about 3.18 and 12.70 mm in length, and preferably about 6.35 mm. The diameter of the glass fibers should be between about 2 and about 8 µm, and preferably between about 3 and about 5 µm. It is believed that the smaller diameter fibers provide better (i.e. faster) wettability. It is also believed that, in separators using fibers of large diameter, the ratio of the binder to the specific surface of the fibers, for a fixed quantity of binder, becomes higher and therefore somewhat reduces the ability of the separator to absorb very quickly a liquid. Glass fibers having a diameter of less than 2 µm are generally too small to provide the mechanical strength and handling characteristics desired for low levels of binder, i.e. 15% by weight or less of binder. The length of the fibers seems to be important for good wettability characteristics for the separator. In particular, uniformity in the length of the glass fibers is of primary importance, as it is believed that a wide variation in the length of the glass fibers can result in a distressed or uneven appearance, which may result in a non-uniform absorption of the liquid cathode, leading to the drawbacks indicated above.

The binder which is preferable to use in the manufacture of the separator should be a polyvinyl alcohol binder, as it is believed to promote a higher wetting speed of the separator. Other suitable binders could be polyvinyl acetate, polyvinyl chloride and polymers of polyvinyl acetate and polyvinyl chloride.

The separators used in the context of the present invention can be produced by conventional papermaking techniques, that is to say by preparing a suspension of the fibers, casting the suspension in sheets, then rolling and drying of the sheet cast. Short glass fibers, less than 6.35 mm; may tend to clump, giving a distressed appearance to the upper surface of the leaf. Thus, when the sheet is then laminated, these agglutinations are more compressed than the surrounding areas, and it is believed that these denser compressed areas tend to be wetted at a lower speed or not to be wetted at all. The more uniform length of the glass fibers promotes a more uniform distribution of the glass fibers in the sheet and therefore more uniform and faster wetting characteristics of the resulting separator.

The thickness of the separator is generally between approximately 0.051 and approximately 0.254 mm, preferably between approximately 0.127 and 0.178 mm. A separator thickness less than 0.051 mm tends to be ineffective due to shorting of the anode on the collector, while a thickness greater than 0.254 mm tends to excessively increase the internal resistance of the battery. Separators suitable for the invention can be obtained from Crane & Company, Inc., Dalton, Mass., Under the trademarks Craneglas 200, Craneglas 210 and Craneglas 230.

The preferred separator has the following characteristics: thickness of the separator: 0.127 to 0.178 mm (preferably 0.127 mm),

fiber diameter: about 3 to 4 (im,

fiber length: about 6.35 mm (uniform),

type of binder: polyvinyl alcohol,

binder content: 7-8% by weight (evenly distributed at the fiber junctions),

uniformity of absorption: highly uniform,

preferred absorption rate at 20 ° C: less than approximately 10 s for a drop of water of 0.20 ml to be absorbed on the surface of the separator, preferred capillary ascent rate at 20 ° C: regularly less than approximately 45 s, preferably about 25 s or less required from water to rise 25.4 mm on a separator sheet, the lower part of which is immersed in 25.4 mm of water.

Nonaqueous liquid cathode materials suitable for use in batteries according to the invention may include sulfuryl chloride, thionyl chloride, phosphorus oxychloride, thionyl bromide, chromyl chloride, vanadyl tribromide , selenium oxychloride, sulfur monochloride, sulfur monobromide, selenium tetrafluorare, selenium monobromide, thiophosphoryl chloride, thiophosphoryl bromide, vanadium pentafluoride, lead tetrachloride, tetrachlor titanium, sulfur pentafluoride, tin monobromuretrichloride, tin dibromuredichloride, tribromuremon tin chloride and mixtures of these materials. Another suitable cathode material could be liquid sulfur dioxide.

The anode to be used in the batteries according to the invention can generally consist of consumable metals and can include alkali metals, alkaline earth metals and alloys of alkali metals or alkaline earth metals, with each other and with other metals. The term alloy used here is intended to include mixtures; solid solutions such as lithium-magnesium, and intermetallic compounds such as lithium monoaluminide. The preferred anode materials are the alkali metals and in particular lithium, sodium and potassium. When lithium anodes are used, the anode can be coated with a vinyl resin as described in US Patent No. 3,993,501, said patent being incorporated herein by reference.

The cathode collector to be used in batteries suitable for the invention must be electronically conductive in order to allow the establishment of external electrical contact with the material of the active cathode and also to provide extended surface reaction sites for the electrochemical process of cell cathode. Materials suitable for use as a cathode collector are materials containing carbon and metals such as nickel, with acetylene black being preferable. In addition, the cathode collector, when made of a particulate material,

must be capable of being molded directly into a housing or should be capable of being molded into separate bodies, of various dimensions, capable of being handled without cracking or breaking. To impart a cohesive characteristic to certain types of cathode collectors such as carbonaceous cathode collectors, a suitable binder, with or without plasticizers and with or without stabilizers, can be added to the materials of cathode collectors. Binders suitable for this purpose may include polyvinyl, polyethylene, polypropylene, polyacrylic resins, polystyrene and the like. For example, polytetrafluoroethylene may be the preferred binder for cathode collectors for use with liquid oxyhalide cathodes. If necessary, the binder should be added in an amount between about 5 and about 30% by weight of the molded cathode collector, since an amount less than 5% does not give sufficient resistance to the molded body, while an amount greater than 30% makes the surface of the carbon impermeable and / or reduces the usable surface of the carbon, thereby reducing the areas of activation sites necessary for the cathodic electrochemical process of the cell. Preferably, the

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binder should be between 10 and 25% by weight of the cathode collector. It is important, when selecting materials for the cathode collector, to select materials that are chemically stable in the cell system in which they are to be used.

The solute to be used in batteries suitable for the invention may be a single or double salt which produces an ionically conductive solution when dissolved in a suitable solvent. Preferred solutes for nonaqueous systems are complexes of mineral or organic Lewis acids and ionizable mineral salts. The only requirements for use are that the salt, whether simple or complex, is compatible with the solvent used and that it gives an ionically conductive solution. According to the electronic or Lewis concept of acids and bases, many substances that do not contain active hydrogen can behave like acids or acceptors of electronic doublets. The basic concept is given in the chemical literature ("Journal of the Franklin Institute", vol. 226, July / December 1938, pp. 293-313, by G.N. Lewis).

A suggested reaction mechanism for how these complexes act in a solvent is described in detail in US Patent No. 3542602 where it is suggested that the complex or double salt formed between Lewis acid and the ionizable salt gives an entity which is more stable than either of the components considered alone.

Typical Lewis acids suitable for use in the present invention include aluminum fluoride, aluminum bromide, aluminum chloride, antimony pentachloride, zirconium tetrachloride, phosphorus pentachloride, boron fluoride, boron chloride and boron bromide.

Ionizable salts useful in combination with Lewis acids include lithium fluoride, lithium chloride, lithium bromide, lithium sulfide, sodium fluoride, sodium chloride, sodium bromide, sodium fluoride potassium, potassium chloride and potassium bromide.

It is obvious to those skilled in the art that the double salts formed by a Lewis acid and an ionizable salt can be used as such, or the individual constituents can be added to the solvent separately to form the salt or resulting ions in situ. One such double salt, for example, is that formed by the combination of aluminum chloride and lithium chloride to give lithium aluminum tetrachloride.

If desired, and in particular for halides, a co-solvent should be added to the reducible active liquid cathode and to the solute solution to modify the dielectric constant, viscosity or solvent properties of the solution in order to get better conductivity. Some examples of suitable co-solvents are nitrobenzene, tetrahydrofuran, 1,3-dioxolane, 3-methyl-2-oxazolidone, propylene carbonate, y-butyrolactone, sulfolane, ethylene glycol sulfite, dimethyl sulphate, 5-benzoyl chloride, dimethoxyethane, dimethylisoxazole, diethyl carbonate, sulfur dioxide and others.

The battery container could be made of stainless steel, iron, nickel, plastic, coated metals or any other suitable material.

Some preferred combinations of non-aqueous cathode and anode materials could be as follows:

1) sulfuryl chloride / Li or Na;

2) thionyl chloride / Li or Na;

3) phosphorus oxychloride / Li or Na;

4) sulfur monochloride / Li or Na;

5) sulfur monobromide / Li or Na;

6) selenium / Li or Na tetrafluoride.

Preferably, the batteries to be used in the invention should be liquid oxyhalide batteries using sulfuryl chloride, thionyl chloride or their mixtures with a lithium anode.

2s Example I:

Several 12.065 mm diameter batteries (lot A) were produced, each with a lithium anode, a cathode collector in acetylene black bonded with Teflon and an electrolyte solution comprising a thionyl chloride liquid cathode containing 1 , 5 M of 30 LiAlCl4. A 0.127 mm thick non-woven glass fiber separator obtained from Crane & Company, Inc., Dalton, Mass. under the trade name Craneglas 200, was placed between the anode and the cathode collector of each cell. The separator had a uniform distribution of about 93% glass fibers, each about 6.35 mm long, and a diameter of about 3.5 µm, and about 7% by weight of a binder made of polyvinyl alcohol. Several similar stacks (lot B) were produced each with the same constituents as above, except that the separator of each stack had a uniform distribution of approximately 96% by weight of 40 glass fibers, each having approximately 6.35 mm in length and a diameter of about 0.5 to 0.7 ^ m, and about 4% by weight of a (poly) acrylic binder. The batteries in each batch were charged (excessive charge test) at different currents, as shown in Table 1, until they produced gases. The production of 45 gases from each cell was observed and classified as shown in Table 1.

Table 1

Lot A

Lot B

Battery

Charge

Observation

Battery

Charge

Observation

(AT)

(gas emission)

(AT)

(gas emission)

1

1.0

* No gas emission

1

1.0

Whistling noise

2

1.0

* No gas emission

2

1.0

** Moderate noise

3

1.8

Smell only, no noise

3

1.0

** Moderate noise

4

1.5

Smell only, no noise

4

1.0

** Moderate noise

* The battery was recharged to 1.5 A and produced a gaseous emission for which only an odor was observed, without any noise. ** The moderate noise was louder than the hissing noise.

As is evident from the data in Table 1, the separator according to the invention has a safety characteristic when it is used in lithium / oxyhalogenated battery systems, subjected to abusive conditions.

Example II:

Several batteries from batch A and batch B were produced as in Example I. Each battery was discharged through a specific charge, at a cut-off voltage of 2.7 V, after which the quantity of lithium remaining in the stack, as well as the deli-65 power output of each stack, were recorded and are given in Table 2. A transducer was placed under each stack, then the flame of a laboratory gas burner was aimed at the stack. The maximum force recorded during the gas emission of each

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cell was observed and is indicated in table 2. The data indicated in table 2 clearly show the results above Example III:

Three stacks of lot A and three stacks of lot B were made as in Example I. The stacks of each lot were stored at 71 ° C.

As is shown by the data indicated in Table 3, the behavior of the cells using the separator according to laughers which can be obtained in a liquid cathode cell using the separator according to the invention.

for a month, then were discharged through a charge of £ 75 2, and the voltage observed for each battery was recorded. The average voltage observed for three batteries in each batch of batteries, as a function of time, is given in table 3.

the invention was much superior to the behavior of batteries using separators.

Table 2

Charge (£ 2)

15

25

35

50

75

250

Approximate battery flow (Ah)

0.22

0.32

0.50

0.60

0.78

1.18

Approximate grams of Li remaining

0.27

0.25

0.20

0.17

0.13

0.02

Gas emission force (N)

Number of batteries in lot A

About 155.75

0

0

0

0

0

0

About 53.4

2

2

1

2

1

0

About 22.25

3

3

3

1

1

1

Gas emission force (N)

Number of batteries in lot B

About 155.75

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3

2

2

1

0

About 53.4

0

1

1

2

2

1

About 22.25

0

1

2

1

2

1

Table 3

Time (s)

Lot A

Lot B

Voltage (V)

Voltage (V)

0.8

2.38

2.00

1.0

2.40

2.20

3.0

2.80

2.44

5.0

2.85

2.62

7.0

2.88

2.73

9.0

2.90

2.81

R

Claims (11)

653,808 1. A non-aqueous cell comprising a liquid cathode, an active anode, a cathode collector and a separator arranged between said anode and said cathode collector, characterized in that the separator comprises a uniform mixture of 85 to 95% by weight of glass fibers and 15 to 5% by weight of binder, said glass fibers having a length of 3.18 to 12.70 mm and a diameter of 2 to 8 µm, and in which at least 90% of the fibers glass differ by less than 20% from the average length of the glass fibers and differ by less than 20% from the average diameter of the glass fibers. 2. A non-aqueous cell according to claim 1, in which at least 95% of the glass fibers differ by less than 20% from the average length of the glass fibers and by less than 20% from the average diameter of the glass fibers. 2 3. A nonaqueous cell according to claim 1, in which at least 95% of the glass fibers differ by less than 10% from the average length of the glass fibers and by less than 10% from the diameter of the glass fibers. 4. The non-aqueous cell according to claim 1, wherein the glass fibers have a length of about 6.35 mm and a diameter of between about 3 and 4 µm. 5. A nonaqueous cell according to claim 1, in which the binder is chosen from the group comprising polyvinyl alcohol, polyvinyl acetate, polyvinyl chloride and polymers of polyvinyl acetate and polyvinyl chloride . 6. A nonaqueous cell according to claim 1, in which the glass fibers constitute 91 to 94% by weight of the separator and the binder constitutes 6 to 9% by weight. 7. Non-aqueous cell according to one of claims 1,4, 5 or 6, wherein the separator has a thickness between 0.051 and 0.254 mm. 8. A non-aqueous cell according to claim 7, in which the separator has a thickness of between 0.127 and 0.178 mm. 9. A non-aqueous cell according to claim 7, in which the liquid cathode comprises at least one liquid oxyhalide chosen from the group consisting of thionyl chloride, sul-furyl chloride, phosphorus oxychloride, thionyl bromide, chromyl chloride, vanadyl tribromide and selenium oxychloride. 10. The nonaqueous cell of claim 9, wherein the liquid oxyhalide is thionyl chloride. .11. The non-aqueous cell according to claim 7, wherein the anode is selected from the group comprising lithium, sodium, calcium, potassium and aluminum.